Pressure applying mechanism



Nov. 25, 1952 J. ,c. CANTLEY 2,618,931

PRESSURE APPLYING MECHANISM Filed-Aug. 2, 1950 2 SHEETSSHEET l Invcnfar Jbseph 00012275 Nov. 25, 1952 J. c. CANTLEY 2,618,931

PRESSURE APPLYING MECHANISM Filed Aug. 2, 1950 2 SHEETS-SHEET 2 Invenfar Jbseph G fianzl y By his filzfor'ney Patented Nov. 25, 1952 UNITED STATES TENT OFFICE PRESSURE APPLYING MECHANISM Application August 2, 1950, Serial No. 177,311.

10 Claims. 1

This invention relates to pressure applying mechanisms, and is illustrated herein as embodied in a fluid pressure operated machine for applying pressure to shoe bottoms, as illustrated and described in United States Letters Patent No. 2,459,845, granted January 25, 1949, to T. H. Seely et al., but it will be understood that the invention is not thus limited in its application.

It is an object of the invention to provide an improved machine of the type referred to above having provisions for safeguarding the operator against injury.

The Seely et al. machine includes a rotary distributor valve which is turned 45 upon each depression of a treadle to cause simultaneous admission of pressure fluid to one station of the machine and exhaust of the fluid from the other station. Admission of pressure fluid to one station of the machine causes a sole supporting pad to be raised thus moving a shoe on the pad into engagement with heel and toe abutments and then to exert pressure through the pad on the shoe bottom. Pressure fluid is first admitted into a cylinder housing a small piston causing rapid upward movement of the pad box and after the shoes moves into engagement with the abutments the pressure fluid operates a large piston to obtain the final high pressure. The operator places the shoe on the pad and then steps on the treadle and there is always a danger that unless his hands are removed from over the shoe and last before stepping on the treadle they may be caught between the last and one of the abutments causing severe injury to the hands. To eliminate this hazard, and in accordance with a feature of the invention, a pair of manual controls is provided which requires the use of both hands of the operator before pressure suflicient to injure the operator is applied to the work. These manual controls are employed in conjunction with the treadle, provision being made in accordance with a further feature of the invention for moving the pad box upwardly under sufficient pressure to bring the shoe into engagement with the abutments, the pressure not being substantially greater than that required to lift the pad box and the work thereon so that should the operator have his hand on the top of the last no injury will occur. It is desirable that; initial upward movement of the pad box be under the control of the treadle so that the operator may hold the shoe in place if he so desires until it is clamped against the heel and toe abutments. After this initial clamping pressure has been applied which, as

stated above is insufficient to cause injury to the operator, the application of additional pressure requires that both manual controls be operated simultaneously which necessitates the use of both hands of the operator. With this arrangement both hands of the operator are available to hold or move the work at all times until it is clamped by the heel and toe abutments after which there is no necessity for the operator to handle the work further, but both hands must be removed from the danger zone and engaged with the manual controls before any substantial pressure may be applied by the machine to the Work.

Provision is made in accordance with a still further feature of the invention to insure that both manual controls must be operated during each cycle of operation of the machine, that is, they must each be depressed and then released and the machine cannot be operated if either one or both of the controls are tied in the pressureapplying positions.

The above and other features of the invention, including various details of construction and novel combinations of parts will now be described by reference to the drawings and pointed out in the claims.

In the drawings,

Fig. 1 is a front elevation, partly in section, of a portion of one form of machine in which the invention is embodied; and

Fig. 2 is a schematic View of the fluid pressure system of the machine.

The invention is illustrated as embodied in a machine having a base in the form of a housing l9 carried by and depending from the top wall l2 of which is a pair of fluid pressure motors it, one at each side of the machine and located within the housing I9. Each of the motors comprises a large cylinder l6 and a small cylinder [8 in which are vertically movable large and small pistons 26 and 22 connected for conjoint movement. Each of the large pistons projects upwardly through the top of the housing and carries a yoke 2 in which is carried a work supporting member 25 which may be in the form of a pad box for supporting a sole and lasted shoe. Also, as shown in the Seely et al. patent the machine is provided with a pair of holddo-wn members against which the lasted shoe is forced by the upward movement of the pad box to exert pressure on the bottom of the shoe, these holddown members being carried by an upwardly extending supporting post 26.

Supported in the lower part of the housing I9 is a reservoir 28 for oil or other suitable pressure fluid by which the machine is operated. Oil is drawn from the reservoir by a pump 36 driven by a motor 32 mounted on a cover plate 34 secured to the top of the reservoir. A rotary valve 35 (Fig. 2) directs pressure fluid to one or the other of the fluid pressure motors 14 depending upon its position and it is rotated 45 upon each depression of atreadle 38 to admit pressure fluid into one of the fluid pressure motors and to exhaust it from the other. The treadle 38 is connected by a link 40 to one arm of a bell crank lever 42, the other arm of which has pivoted to it a rod 44 which cooperates with a ratchet 46 connected to the valve 36 so that unoneach depression of the treadle 38, the valve 36 turns 45] in a counterclockwise direction. A spring 48 acting between the top of the reservoir and a. collar 50 secured to the link 40 normally maintains the treadle in its upper position as illustrated. Provision is also made for moving the valve 36 into an n ermediate. posi o so hat. ro -s r fl i a ts from bo h of the lui rossu o mo ors in the. event that the pump is sh t ow and for preventing actuation of the, valve by the treadle 38 until the pump is again started. This consists of a cylinder 52 connected to the high pr ssure side. of he pump ont ning a iston' normally urged upwardly but held in the down position hen e pum is o a n Pivoted to a bracket 55 at the lower end of the piston 5A is an upward y ext nd n member 58. carrying a pawl 6.0 which. whe h pump is sh t down and the. piston. 54 is m v d upw rd y. turn the ratchet 46 2.2 /2" t x au b th of t e. id. pressure mofiors. At this time the rod id which passes through a slot in the upper end of the member. 58. is. lifted out Of Operative relation to the. ratchet 46. so. a e va ve cann be 1 6 71 ated upon depression, of the treadle until the pump is again started and the mBtmber 58 moved: downwardly. ese. features thus far rei r ed to are described in greater. detail in the Seely et a1. patent.

Carried by the top [2, of the housing ID is a pair of valve housings 62, 6d containing valves to be described to which are connected buttons 66., 68v by which, the operator can depress the valves. In the normal operation of the machine the operator depresses thetreadle 3B. rotating the distributor valve 3tfto connect one of the cylinders [8 to the outlet of the pump and to exhaust the pressure fluid, from the other motor M, as willbe more. fully explained, whereupon one of. the work, supports moves upwardly. The res-v sure Of. theoporating fluid by wh h the s pp rt is moved upwardly, is limited by a relief valve contain d in, a manifold 10, the valve being ad.- justed to limit the pressure of the fluid to that which is required to raise the work support with. the work thereon. Thus if. the operator should inadvertently leave his hand between the work and the hold down. members insuflicient pressure will be appliedto cause him any injury. In order to apply operating pressure to the work it is nec.

' essary that the operator. depress both buttons. 66,

68, the valves 62, 64 being connected in series, whereupon the full operating pressure will be applied to the work as will be described.

The fluid pressure system will now be described by reference. to Fig. 2. Those portions of the fluid. pressure system except for the motors [4 which are duplicatedin the two stations of the machin are identifiedby similar reference characters but those on the'left are provided with a prime. It will be assumed that the valve 36. has been moved by the treadle into the position shown in Fig. 2. This movement of the valv permits flow of fluid from the pump 30 through pipes i2, M, 16, the chamber of valve 36, pipes 18, 86, 82 and through a port 84 of the cylinder [8 to act upon the small piston 22 and force the work support upwardly. The pressure applied to the small piston 33 is limited at this time by a relief valve 86 to that which is suflicient to move the support and the Work upwardly. This valve includes a valve member 88 which is urged toward the left by a light spring 90 the action of which may be regulated by an adjusting screw 92. When the pressure of the fluid in the left end of the valve 86 attains a predetermined value, the valve member 88 moves to the right against the spring 90 permitting exhaust of fluid through a port 94 and a pipe 96 which conducts the fluid back to the reservoir 28. The valve 86 has an inlet port connected by a pipe 98 to a. pres u e on o al e h in a valv em e '92 ur by a. sa i e "1 to th lo t he po t n. s ows n 2-. he ipe t is ncei d. y P p i l-5 o he a ve i ed. wi h. e alve memb 1 2 the o i i n shown. uid Passe awh le a d-1. 969 Port on o the.- valve membe o p pe 55 nd he c n o. t e lioi: alve- A oQ Psly with-tho. v re monster 1- 2.- i he Po n th pr ss r o t e ui i ho ov ii or t s imi ed. v the re ie alve it o. as th s r ai b e. t mato t e shoe support upwardly is insufiicient to. ca se to the operator.

2 Pip so; has; a orrect on t on and oils-i s o a le or valu "1 which. is. m nt v l m mb r- I it ic s umes. ho. PtiFiQfl how i Fi th. he. va v he. osit on i tra od.-. f; ow.- hs. alve 1 moved. hrou h. in a e i by tho.- no e t r d p ess.- s. h ad e ho'fi i l ws hrou Pioos; 1- B to he o t and o t al M1 o hift ho. valve. member into. its other p0$il ion. It will; be. i'iq r toqd. ha fluid. oo mitto o xhaust; f qm ne nd i h al I Q wh n s oppo i e nd. s: nn c e t a s urc o erasure... hrou h. ip s 2 H4; ch Q lQllQ e pressur lui e f o he r ser Ehottwme o ho.- so os.- or valve ito ont lth flo o lu-i tho i ohe a ve t-o lv W l d oeeoin i a hioh station. of the machine is being operated, as will; be described. to operate. the valve 1 00; or; IQQ! and r n lhs i valv r. 8. o ioo vo-I Eor moving the pressure Connor valve-168, the other pressure controhvalve m6, pressure fluid accumulator I ITS isprovided. This accum 1 lator includes a cylinder. having a piston ll-8;- urged upwardlvby a spring. I26, The upper end of. the cylindeijfis maintained, filled. with pressure fluid aslong as the buttons 6.6;, '68 of th fcontrol valves 62, arein the. positions illustrated. These buttonsareconnectedby stems. I22, l 24 .to valve members I26, I23 whi" ch are. normally maintained in their 'upper positions. by. springs [36,, I3 2 With thevalvesinthesepositions the; pipe.1.2 connectedtothe high. pressure. side of. the pump 3.01s connected through. a. check valve; I34, andapipe 1.36 to theupper-portion of the-.charn.-. ber.v of valve .62 which is; in turn connected by. a pipe IBBtQtheupper portion of. thechamher of, valve 6 4.. A pipe I411 provides. communication be; tweentheupper end. of. the ch amber of valve 64, and theaccumulator I 1.6 so that as. long. as; the valvemembers, I26, l2 t l r e nain in theirfuppfire m t-ho it nshe .199 1 ort on i h ooumiir a r willhe mai ta ned filledwi h rossur lfiuid In order to insure that no air is trapped within the upper end of the accumulator a pipe I42 having a restriction I44 therein provides communication between the accumulator and the fluid reservoir so that pressure fluid flows continually through the accumulator and any air which might be trapped therein will pass through the pipe I42 back to the fluid reservoir. The flow through the pipe I42 is retarded by the restriction I44 so that when it is desired to utilize the pressure fluid in the accumulator to operate one of the pressure control valves I00, I80 there will be no substantial loss of pressure fluid through the pipe I42.

If the valve members I26, I28 are now simultaneously depressed against the actions of the springs I80, I32 the supply pipe 12 will be cut off from the accumulator and the pressure fluid in the accumulator will be forced by the piston I I8 through the pipe I40, the valve 64 and pipe I46, the valve member 62 and a pipe I40 into the selector valve I66. With the selector valve member H0 in the position shown the pressure fluid will then pass through a pipe I56 into the left end of the chamber of valve I08 by way of a port IBI and passage I52 in the valve member I62, thus acting on the valve member to move it to the right against the action of the spring I64. As soon as the valve member I02 has moved a short distance pressure fluid flows from the pipe I06 through a pipe I68 into the extreme left end of the valve I06 so that pressure from the pump is available to complete the movement of the valve I00 and hold it in its right-hand position as long as the right-hand station of the machine is under pressure. To prevent premature operation of valve member I62 which might occur if pressure fluid from pipe I66 leaked into the left end of the cylinder I66, the bore I52 communicates by way of a port I65 with a pipe I51 which conducts the fluid back to the reservoir with the valve member I62 in the position illustrated. It will be understood that only sufficient pressure fluid is stored in the accumulator to initiate action of the valve member I02 but that the pressure from the pump holds the valve member in its righthand position once it has been so moved. In order to store fluid in the accumulator for similar operation of the valve I00 after the machine has been treadled and valve 36 moved 45, both valves I26 and I28 must be released to connect the upper end of the accumulator with the high pressure side of the pump. Thus if either one or both of the valves I26, I23 should be held down the left-hand side of the machine cannot be operated under any greater pressure than that permitted by the relief valve 66. Once, however, that the pressure control valve I00 has been moved against the action of its spring, communication between the high pressure side of the pump and the relief valve 86 is interrupted and additional pressure is available to operate on the workpiece as described in connection with valve I08.

Connected to the pipe 12 is a pressure regulating valve I64 having a valve element I56 urged downwardly by a spring I58 to control the maximum amount of pressure in the pipe 12. This valve is preferably set to open only after the pressure reaches a relatively high value such as 180 to 190 pounds per square inch which will be the pressure acting upon the small piston 22 after the two hand control valves have been operated. The outlet of the pressure regulating valve I54 is connected by pipes I60, I62 to the chamber of a valve I64 in the lower end of the cylinder I8.

This valve includes a valve member I66 urged upwardly by a spring I68 into the position shown in Fig. 2 in which communication between the pipe I62 and a passageway I10 leading into the large cylinder I6 is cut off. However, when the pressure below the piston 22 reaches a predetermined value the valve member I66 will be forced downwardly by the pressure acting thereon permitting pressure fluid to flow into the passageway I10 and into the large cylinder I6 to act upon the large piston 20 applying the final pressure to the work. During initial upward movement of the pistons pressure fluid is drawn into the large cylinder l6 by way of passageway I10 and pipe I12 which is connected to the fluid reservoir. A pipe I14 provides communication between the reservoir and the upper en-dof the cylinder I8 so that in the event the machine is: operated with no work on the work support the piston 22 will uncover a port communicating with the pipe I14 before the pistons have been forced upwardly too far permitting the pressure fluid to flow back by way of pipe I14 to the reservoir.

The pressure of the fluid applied to the large piston 20 is regulated by a valve I16 having a valve member I18 urged downwardly by a spring I the force of which is controlled by an adjusting screw I62. A pipe I84 provides communication between the pipe I60 and the bottom of the valve I16 so that when the pressure in the pipe I60 attains a predetermined value the valve member I18 is forced upwardly permitting fluid to pass through pipes I86, I88 back to the fluid reservoir. The valve I16 is preferably set at any desired pressure between limits of say 25 and 200 pounds per square inch, it being understood that the pressure per square inch against the piston 20 may be substantially less than that which is available for forcing the piston 22 upwardly.

It is essential that the valve members I26, I28 be held down for a long enough time to permit the fluid in the accumulator to act upon the pressure control valve I60 or I00. Provision is therefore made for preventing return movement of these valve members too rapidly in the event that the operator should only momentarily keep his hands on the buttons 66, 66. Below each of the valves 62, 64 is a chamber I81 connected by pipes I89, I90 to the fluid reservoir. Communication between the chambers I86 and the valve chambers 62, 64 is controlled by a valve member I62 normally urged upwardly by a spring I94, the valve member being provided with a small central orifloe through which fluid can pass at all times. Upon downward movement of the valve members I26, I28, the valve members I02 are forced downwardly against the action of the springs I04 and immediately return into their closed positions when the movement of the valve members I26. I28 stops. Fluid now can flow into the lower ends of the valve chambers 62, 64 only through the restricted orifices in the valve members I02 so that a dashpot eifectresults and the valve members can return only slowly to their upper positions. The lower portion of the accumulator H6 is connected by pipes I66, I90 tothe fluid reservoir so that the lower end of the accumulator is always maintained full of motive fluid.

In describing the operation of the machine it will be assumed that the station at the right side of the machine has been under pressure, that a work piece has been placed in the station at the left side of the machine to be operated upon and that treadle 38 is depressed to turn the valve 36, 45 from the position shown in Fig. 2; Pipe 82 which communicates with the cylinder I8 at the right side of the machine is now placed in communication with the reservoir through pipes 80, I8, 2 and H4 whereupon the pressure in the cylinder drops and the valve member I66 moves into the position illustrated. Fluid in the large cylinder I6 now passes through pipes I12, I14 to the reservoir whereupon pistons 20, 22 descend by gravity lowering the work support and permitting removal of the Work piece thereon.

At the same time pressure fluid passes through pipes 12, I4, 16,- 18', 89 and 82' into the small cylinder I8 at the left side of the machine, whereupon the fluid acts upon the small piston 22 to raise it and the large piston 20 until the work is clamped between its support and the holddown members, the pressure being limited by the relief valve 85 so that no injury will occur to the operator if his hand should be caught between the work and the holddown members. If the work is not properly positioned on the work support it can be moved by the operator because it is clamped under very light p essure.

Pressure fluid also passes from the pipe 80' into the left end of the selector valve I88 to move the valve member to the right, the fluid in the right end of this valve exhausting through the valve 36 to the reservoir. If now the buttons 66, 83 are depressed by the operator the pressure fluid in the accumulator H6 is forced by upward movement of piston H8 under the action of spring I28 through pipes I48, I46; M8, 59' into the right end of the pressure control valve Hill by way of port 151' and bore I52. The valve member I62 is now moved to'the left and after it has moved a slight distance the right end of the housing of the valve is placed in communication by way of pipe I53 with pipe I08 through which pressure fluid is forcedrby the pump thus to maintain the valve element I62 inits left-hand position cutting ofl flow tothe low pressure relief valve 86'. The pressure within the small cylinder I8 at the left side of the machine now increases to a valuedependent upon the setting of the valve I54 andafter this pressure rises to apredetermined value 'the valve member I66 is moveddownwardly against the action of the spring I58 whereupon pressure fluid flows from the pipe 162 into the passagewayIlB leading to the large cylinder I6 and heavy pressure; limited by the setting of the relief valve I16, is applied to the work.

The pressure remains on the work in theleft side of the machine until the distributor valve 36 isagain turned through an angle of 45 and in order for the right-hand side of the machine to be operated under high pressure the buttons 66, 68-must be released permitting the valve members I26, I28 to assume the positions illustrated and permitting pressure fluid to pass into the upper-end of the accumulator H6; Thus if the operator attempts to render the machine unsafe by tying down either or both of the buttons 68 he will be unable to operate the' machine.

From the above it willbe seen that by stepping on the treadle the work piece may beclamped under very light pressure during which time the operator may hold the work and move it if necessary so that it will be properly positioned on. the-work support but he must remove his hands from the work and operate the two buttons 66, 68 in order to :apply heavy pressure to the work. Thus his'h'ands are available to insure that the work is properly positioned for the pressure applying operation but this operation cannot be initiated until his hands are removed from the danger zone.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, fluid pressure operated means for thus moving said member, a pump, a supply pipe for delivering pressure fluid from said pump to said fluid pressure operated means, operator controlled means for connecting said pump to said supply pipe, a relief valve connected to said supply pipe to limit the pressure of the fluid therein to a low predetermined'value, and means for interrupting the flow of pressure fluid from said supply pipe through said relief valve, said last named means comprising a pair of serially connected manually operated valves.

2. Pressure applying mechanism comprising a member movable to apply pressure to a Work piece, fluid pressure operated means for thus moving said member, operator controlled means for directing fluid to said fluid pressure operated means to move said member into pressure applying position, a relief valve operative to limit the pressure of the fluid to a low predetermined value, a fluid pressure operated valve controHing flow of fluid from said fluid pressure operated means to said relief valve, means urging said flow control valve into open position, and means connecting an end of said flow control valve to a source of fluid pressure to move said valve to closed position, said last named means including a pair of manual controls simultaneous operation of which is required to connect said flow control valve to the source of fluid pressure.

3. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, fluid pressure operated means for thus moving said member, means for'directing pressure fluid to said fluid pressure operated means, a low pressure relief valve connected to said fluid pressure operated means, a member operative in response to the application of fluid pressure thereto for rendering said low pressure relief valve ineffective, and a pair of serially connected manually operated valve members for controlling the application of fluid pressure to said member.

l. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, fluid pressure operated means for'thus moving said member, a low pressure relief valve for limiting the pressure of the fluid applied to said fluid pressure operated means, a second fluid pressure operated member for rendering said re-' lief valve ineflective, means for directing pres sure fluid to said second fluid pressure operated member for moving said member into operative position, and a pair of spaced serially connected manually operated valves in control of said last named means.

5. Pressure applying mechanism'comprising a member movable to apply pressure to' a work piece, fluid pressure operated means for thus moving said member, a low pressure relief 'valve for limiting the pressure of the fluid applied to said fluid pressure operated means, a second fluid pressure operated member movable into operative position in which it renders said 'relief valve ineffective, a fluidpressure accumulator, a pair of spaced manually operated valves, means operative with said valves in first predetermined positions for directing pressure fluid to said accumulator, and means operative with said valves in second predetermined positions for directing the pressure fluid in the accumulator to said second fluid pressure operated member to move the member into operative position whereby the pressure applied to the work piece exceeds the pressure at which said relief valve is set.

6. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, fluid pressure operated means for thus moving said member, a low pressure relief Valve for limiting the pressure of the fluid applied to said fluid pressure operated means, a second fluid pressure operated member movable into operative position in which it'renders said relief valve ineflective, a fluid pressure accumulator, a pair of spaced manually operated valves, means operativ with said valves in first predetermined positions for directing pressure fluid to said accumulator, means operative with said valves in second predetermined positions for directing the pressure fluid in the accumulator to said second fluid pressure operated member to move the member into operative position whereby the pressure applied to the work piece exceeds the pressure at which said relief valve is set, and other means for directing the pressure fluid to said second fluid pressure operated member following return movement of said valves to the first predetermined positions.

7. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, a small piston for moving said member rapidly into pressure applying position, a large piston for exerting heavy pressure on said member, a small cylinder and a large cylinder housing said small and large pistons respectively, means for supplying pressure fluid to said cylinders including a pump, a low pressure relief valve for limiting the pressure of the fluid in the small cylinder to a low value, a main control valve for directing pressure fluid to said small cylinder, a pair of spaced manual control members, means operativ in response to simultaneous actuation of said control members for rendering said low pressure relief valve ineffective, and means operative in response to an increase in the pressure of the fluid in th small cylinder for directing pressure fluid to said large cylinder.

8. Pressure applying mechanism comprising a member movable to apply pressure to a work piece, a small piston for moving said member rapidly into pressure applying position, a large piston for exerting heavy pressure on said member, a small cylinder and a larg cylinder housing said small and large pistons respectively, means for supplying pressure fluid to said cylinders including a pump, a low pressure relief valve for limiting the pressure of the fluid in the small cylinder to a low value, a main control valve for directing pressure fluid to said small cylinder, a fluid pressure operated member movable, in response to the application of pressure fluid thereto, into a position in which the flow of pressure fluid to the low pressure relief valve is interrupted, a pair of spaced manually operated serially connected valves, means operative in response to simultaneous actuation of said valves for directing pressure fluid to said fluid pressure operated member, and means operative in response to an increase in th pressure of the fluid in the small cylinder for directing pressure fluid to said large cylinder.

9. Pressure applying mechanism comprising a pair of pressing stations each of which comprises a member movable to apply pressure to a work piece, a piston connected to said member, and a cylinder housing said piston, a pump, a valve movable into different positions for directing pressure fluid into one or the other of said cylinders, a treadle for operating said valve, a low pressure relief valve connected to each cylinder for limiting the pressure of the fluid therein to a low predetermined value, a fluid pressure operated member associated with each relief valve and operative in response t the application of pressure fluid thereto for rendering the associated relief valve ineflective, a pair of spaced manually operative members, and means operative in response to simultaneous operation of said members for directing the pressure fluid to the fluid pressure operated member of the station which is being operated.

10. Pressure applying mechanism comprising a pair of pressing stations ach of which comprises a member movable to apply pressure to a work piece, a piston connected to said member, and a cylinder housing said piston, a pump, a valve movable into different positions for directing pressure fluid into one or the other of said cylinders, a treadle for operating said valve, a low pressure relief valve connected to each cylinder for limiting the pressure of the fluid therein to a low predetermined value, a fluid pressure operated member associated with ach relief valve and operative in response to the application of pressure fluid thereto for rendering the associated relief valve inefiective, a pressure fluid accumulator, a pair of spaced serially connected manually operated valves, means operative with said valves in predetermined positions for directing pressure fluid to said accumulator, means operative with said valves in other predetermined positions for exhausting the fluid from said accumulator, a selector valve for directing the fluid from said accumulator to one or the other of said fluid pressure operated members, and means for automatically positioning said selector valve in accordance with the station being operated.

JOSEPH C. CANTLEY.

REFERENCES CITED The feilowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,115,414 Davis Apr. 26, 1938 2,394,655 Better Feb. 12, 1946 FOREIGN PATENTS Number Country Date 624,146 Great Britain May 27, 1949 

